A discharge tube in which a reflective film is formed on a cylindrical glass bulb such that a belt-like translucent part for transmitting light are secured is conventionally known as the discharge tube provided on a light emitter of a stroboscopic device (e.g., PTL. 1). The reflective film is formed by metal deposition of typically aluminum or silver to reflect the light generated in the discharge tube for improving luminous efficiency.
FIGS. 11A and 11B are overall sectional views of conventional discharge tube 2. Discharge tube 2 irradiates light outward by light emission of entire gas excited inside glass bulb 9. Accordingly, if reflective film 10 is deposited in a small range (area) on the outer periphery of glass bulb, as shown in FIG. 11A, light emission at point G is not reflected on reflective film 10 and irradiated to the back (a direction different from a required direction) of discharge tube 2. Therefore, the quantity of the light is lost. Contrarily, if reflective film 10 is deposited in a large range (area) on the outer periphery of glass bulb 9, as shown in FIG. 11B, a loss of quantity of light can be prevented, but a light distribution range becomes narrow.
Furthermore, in general, reflective film 10 peels off from the outer periphery of glass bulb 9 in discharge tube 2 in which reflective film 10 is formed.